Surface water is water that collects on top of the Earth's surface, in water bodies such as oceans, lakes, rivers, streams, creek, wetlands, and ice. As seen in the water cycle diagram, surface water is where evaporation occurs from and is where the water that runs off from the land from precipitation collects.

There are three types of surface water:

• Perennial/ permanent = surface water that persists throughout the year, and is replenished by groundwater when there is no precipitation
• Ephemeral/ semi-permanent = surface water that only persists for part of the year
• Man-made = surface water found in artificial structures

Water bodies can persist for a long time, e.g. all year, or for only part of the year. In Ireland, these are called 'turloughs' from the Irish "tur loch" meaning 'dry lake' and is the name given to the 'disappearing' lakes in the limestone bedrock areas of Ireland. Turloughs are interesting, because it is due to groundwater flooding that they become ephemeral, or semi-permanent, surface water bodies. For more information on turloughs, read the 'what is groundwater flooding' page from Geological Survey Ireland's Groundwater Programme page.  

Surface water can be used for a number of different things, such as drinking water, tourism and recreation purposes and for power. In Ireland, most of our drinking water comes from groundwate. Fishing is a popular sport in Ireland's loughs and renewable energy, such as hydroelectric power, can come from dams.

River processes

There are three main types of processes that occur in rivers: erosion, transportation and deposition. These depend on the amount of energy the river has and they, along with the underlying bedrock geology, are responsible for shaping our rivers, riverbanks and river courses and the resulting landforms created.

Erosion

Erosion can affect rivers in three ways – it can make the river longer, the river deeper and the river wider. These scenarios are typical at different stages of the river: the first two (making the river longer and deeper) are more common near the source and upper stages, whilst the last (making the river wider) is more common in the lower and middle stages. Erosion occurs by four erosional processes:

• Hydraulic action – as the river water hits the riverbanks, air is trapped and compressed into the cracks, causing them to expand and eventually collapse.
• Abrasion/ Corrasion – sediment carried by the river scrapes against the riverbed, like sandpaper. This can form potholes, as sediment is scraped in a circular fashion where depressions already exist.
• Attrition – sediments within the river collide and chip against one another, making them become smaller and more rounded.
• Corrosion – weak acids in the river water react with certain rocks, such as limestone and chalk, and erode them by dissolving them.

Where river energy is higher, generally on the outer bends of meanders, is where the most erosion occurs. Where river energy is lower, generally on the inner bends of meanders, is where the most deposition occurs.

Resulting landforms: undercut river banks; outside of meanders; waterfalls; gorges; interlocking spurs.

Transportation

Sediment in rivers can be transported in four different ways:

• Traction – sediments (generally larger) roll along the river bed.
• Saltation – sediments (generally smaller) bounce along the river bed.
• Suspension – sediments, such as is fine particles of silt and clay, are suspended within the water column and moved by the river.
• Solution – sediments, such as minerals, are dissolved in the river water and are moved by the river.

Deposition

Deposition occurs when a river loses its energy and can no longer transport the sediment it is carrying, so deposits it. This can happen when: rainfall is reduced, evaporation rates increase, rivers become shallow, rivers become slow and rivers meet the sea.

Resulting landforms: river beaches; inside of meanders; oxbow lakes; levees; floodplains; estuaries.